In conventional elevator installations having an elevator cage which is displaceable in an elevator shaft, the elevator cage is guided by way of a support means, for example at least one support rope or at least one support belt, said support rope or support belt, respectively, being guided over a drive pulley and deflection rollers and being connected to a counterweight. The elevator cage and the counterweight are displaceable along respective guides in the elevator shaft. The elevator cage is configured having guide rollers which interact with the elevator cage guide.
Moreover, a connection means is connected to the elevator cage. The connection means may be a suspended cable or a support-rope weight compensation means, for example. A support-rope weight compensation means is, for example, a balance chain, a balance belt, a balance strap, or a balance cable. For example, the elevator cage is supplied with electric power by means of a suspended cable. Moreover, data may be exchanged between the elevator cage and an external computer or controller, respectively, by way of the suspended cable. The changing stress by the weight force of the support rope when the position of the elevator cage changes is compensated for by means of a support-rope weight compensation means which connects the elevator cage to the counterweight.
Both the suspended cable as well as the support-rope weight compensation means, as connection means, are typically fastened to the lower side of the elevator cage. Thus, the weight force of the connection means additionally acts on the elevator cage, this potentially leading to non-uniform stresses on the guide rollers of the elevator cage.
The suspended cable is typically fastened to the lower side of the elevator cage, on the one hand, and to or in the elevator shaft, on the other hand. By contrast, the support-rope weight compensation means is typically fastened to the lower side of the elevator cage, on the one hand, and to the counterweight, on the other hand. However, the support-rope weight compensation means may also be fastened to the other side on or in the elevator shaft.
Additionally, the connection means, for example on account of the bending radius of the connection means that has to be adhered to, mostly acts in a decentralized manner, that is to say not on the central region or on the center of gravity of the elevator cage, respectively. Depending on the position of the elevator cage in the elevator shaft, a non-uniform distribution of force and momentum on the guide rollers of the elevator cage is thus created.
In order for good traveling properties and a high level of travel comfort to be guaranteed, the elevator cage must be precisely balanced. Therefore, a compensation mass may be fastened to the elevator cage in order for this variable distribution of force on account of the connection means to be compensated for. On account thereof, a torque which is exerted by the connection means on the guide rollers of the elevator cage, for example, may be compensated for, and the stress on the guide rollers may be reduced.
However, compensation of this type by means of a compensation mass is only optimal in a specific position of the elevator cage, mostly in the center of the elevator shaft. Non-uniform distribution of force on the guide rollers continues to arise in the other positions.
The highest stresses on the guide rollers on account of the non-uniform forces and momentums caused by the connection means arise at the uppermost and lowermost positions of the elevator cage in the elevator shaft. The complete weight force of the connection means acts on the elevator cage and, on account thereof an ultimately undesirable force acts on the guide rollers, in particular in the highest position. On account of the compensation mass, a force which leads to torque and ultimately to an undesirable force on the guide rollers is likewise present in the lowest position.
Alternatively, a symmetrical force acting on the elevator cage may also be achieved by using two connection means on mutually opposite sides of the elevator cage. However, this is associated with high costs and is also often impossible for reasons of space.
Therefore, a need exists for elevator systems that minimize or eliminate stresses that a connection means of an elevator cage exerts on guide rollers of the elevator cage.